Monty Bennett’s name will not appear on the ballot for the Tarrant Regional Water District board of directors yet he remains a powerful backstage player whose influence could shape the direction of the district’s business for years to come.

Chris Brassard and Omar Diaz had apartments in mind when they built a 12-unit complex on May Street just south of West Magnolia Avenue on Fort Worth’s Near Southside. Then their leasing agent, Will Northern of Northern Realty Group, suggested they consider selling the units as condominiums.

Right now, in a high-security research lab at Northwestern University's Falk Center for Molecular Therapeutics, scientists are tickling rats. Their goal? To develop a pharmaceutical-grade happiness pill. But their efforts might also produce some of the best evidence yet that humor isn't something experienced exclusively by human beings.

Scientists believe human laughter evolved from the distinctive panting emitted by our great-ape relatives during rough and tumble play; that panting functions as a signal that the play is all in good fun and nobody's about to tear anybody else's throat out. In a clever bit of scientific detective work, psychologist Marina Davila-Ross of the University of Portsmouth in the United Kingdom analyzed digital recordings of tickle-induced panting from chimps, bonobos, gorillas, and orangutans, as well as human laughter, and found the vocal similarities between the species matched their evolutionary relationships. Chimps and bonobos, our closest relatives, boast the most laughter-like kind of panting, while the noises of gorillas, further down our family tree, sound less like laughing. And orangutans, our truly distant cousins, pant in a most primitive way.

Nonhuman primates don't just laugh — there's evidence they can crack their own jokes. Koko, a gorilla in Woodside, Calif., who has learned more than 2,000 words and 1,000 American Sign Language signs, has been known to play with different meanings of the same word. When she was asked, "What can you think of that's hard?" the gorilla signed, "rock" and "work." She also once tied her trainer's shoelaces together and signed, "chase."

But what about other members of the animal kingdom — do they have funny bones? Marc Bekoff, University of Colorado-Boulder professor of ecology and evolutionary biology and author of "The Emotional Lives of Animals," believes they do. In fact, he thinks we're on the cusp of discovering that many animals have a sense of humor, maybe even all mammals. The idea that animals can appreciate comedy isn't as far-fetched as it sounds, considering some of the other groundbreaking discoveries scientists like Bekoff are making about animal behavior: They have found dogs that understand unfairness, spiders that display different temperaments, and bees that can be trained to be pessimistic.

As Bekoff points out, Darwin argued that the difference between human and animal intelligence is a matter of degree, not of kind. Or as Bekoff put it, "If we have a sense of humor, then nonhuman animals should have a sense of humor, too."

A similar sentiment inspired psychologist Jaak Panksepp to enter his lab at Bowling Green State University in Ohio one day in 1997 and tell undergrad Jeffrey Burgdorf, "Let's go tickle some rats." The lab had already discovered that its rats would emit unique ultrasonic chirps in the 50 kilohertz range when they were chasing one another and engaging in play fighting. Now the researchers wondered if they could prompt this chirping through tickling. Sure enough, when the researchers began poking at the bellies of the rats in their lab, their ultrasonic recording devices picked up the same 50 kilohertz sounds. The rats eagerly chased their fingers for more. Soon, as the news media trumpeted the existence of rat laughter, people the world over were opening up their rat cages and engaging Pinky and Mr. Pickles in full-scale tickle wars.

We met Burgdorf at his office at Northwestern's Falk Center, where as a biomedical engineering professor he's continued his rat-tickling efforts. He was cautious, however, about overselling what's happening with his rodents. "I don't necessarily call it laughter, I call it a signal of positive affect," Burgdorf told us. His careful choice of words makes sense. Not everyone was convinced he and Panksepp had uncovered real rat laughter when their rodent-tickling activities first went public. But whatever you want to call it, Burgdorf, a quick-witted guy with a boyish face and a sign on his office door that reads "Know It All," has been obsessed with that strange rat noise he first heard in 1997.

He seems to be onto something. While tickling isn't always pleasant — thus the term "tickle torture" — in multiple experiments Burgdorf has demonstrated the rats' 50 kilohertz chirping is only associated with positive experiences. For example, the rats only made this sound during rough and tumble play when the animals were of similar size. The vocalizations changed when one of the animals involved was much larger than the other, when it was no longer fun and games and instead looked more like bullying. And when given a choice, Burgdorf's rats would push a bar to play a recording of the 50 kilohertz chirp as opposed to other rat noises, suggesting they had a preference for the sound. Finally, when Burgdorf and his colleagues used electrodes, opiates, and other manipulations to stimulate the reward centers of rats' brains, the rats produced that same laughter-like noise.

Whether you call it laughter or not, Burgdorf is convinced these rats' ultrasonic noises signal they're experiencing happiness. Hence the "laughing pill" experiment: He and his colleagues are testing a new antidepressant medication on rats, to see if it makes them "laugh," or chirp happily. If all goes well, Burgdorf believes the resulting medication could eventually be approved for humans. Rats, so often seen as a malicious pest, could end up making the world a happier place.

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This series is adapted from "The Humor Code: A Global Search for What Makes Things Funny": http://amzn.to/1h0IJvq